The fistfight (Season Four, Episode Nine: "Bug")
One-on-one fights in which seasons' worth of shit explodes to the surface are a grand tradition in long-game TV drama – think Al Swearengen and Seth Bullock on Deadwood, Tony Soprano and Ralph Cifaretto on The Sopranos, Jack Shepherd and every other male character on Lost – but the trick here is that this one provides virtually no catharsis. Jesse's no closer to ridding his life of Walt than he was after all their previous screw-you shoutfests, and Walt's simply that much closer to being totally alone. Even when a wounded, underwear-clad Walt has a devastating heart-to-heart about his situation with Walter Jr. the next day, he still has to lie about who he really is and what really happened to him. In provoking this slugfest, Walter alienates the one person he can really trust, and he'll end up sacrificing anything, and anyone, to get it back.